3GPP Network Architecture
FIG. 1 illustrates an embodiment of a non-roaming architecture for the Evolved Packet System (EPS). A wireless device 101 may interact with EPS using the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 105 radio access. Wireless device related control signaling is handled by a Mobility Management Entity (MME) 108 with support of subscription information provided by the Home Subscriber Server (HSS) 110. User payload is handled by the Serving Gateway (S-GW) 115 and the PDN Gateway (P-GW) 118. The P-GW 118 may interact with a Policy and Charging Rules Function (PCRF) 120. A Serving General packet radio service Support Node (SGSN) 123 is responsible for the delivery of data packets from and to the wireless devices 101 within its geographical service area and provides connections for Universal Terrestrial Radio Access Network (UTRAN) 125 and GSM EDGE Radio Access Network (GERAN) 128 networks. GSM is short for Global System for Mobile communications and EDGE is short for Enhanced Data rates for GSM Evolution. The P-GW 118 provides connectivity to packet data network which may comprise an operator's Internet Protocol (IP) Services 130. The packet data network may be an operator external public or private packet data network or an intra-operator packet data network, e.g. for provision of IP Multimedia Subsystem (IMS) services.
Interfaces are allowing the MME 108, S-GW 115 and the P-GW 118 etc. to cooperate with other network elements (e.g. the HSS 110 or the PCRF 120). An interface may also be referred to as a reference point. LTE-Uu is the interface between the wireless device 101 and the E-UTRAN 105. S1-MME is the interface for the control plane protocol between E-UTRAN 105 and the MME 108. S1-U is the interface between E-UTRAN 105 and the S-GW 115 for the per bearer user plane tunnelling and inter eNodeB path switching during handover. S3 is an interface which enables user and bearer information exchange for inter Third Generation Partnership Project (3GPP) access network mobility in idle and/or active state. This interface is between the MME 108 and the SGSN 123. S4 is an interface between the SGSN 123 and the S-GW 115 and provides related control and mobility support between General Packet Radio Service (GPRS) core network and the 3GPP Anchor function of the S-GW 115. S5 is an interface providing user plane tunnelling and tunnel management between the S-GW 115 and the P-GW 118. It is used for S-GW relocation due to wireless device mobility and if the S-GW 115 needs to connect to a non-collocated P-GW 118 for the required Packet Data Network (PDN) connectivity. The S6a interface enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (Authentication, Authorization and Accounting (AAA) interface) between the MME 108 and the HSS 110. The Gx interface provides transfer of (Quality of Service (QoS)) policy and charging rules from the PCRF 120 to Policy and Charging Enforcement Function (PCEF) in the P-GW 118. S10 is an interface between MMEs 108 for MME relocation and MME to MME information transfer. The interface between the MME 108 and the S-GW is the S11 interface. S12 is the interface between UTRAN 125 and the S-GW 115 for user plane tunnelling when Direct Tunnel is established. SGi is the interface between the P-GW 118 and the Operator's IP services 130. The Rx interface resides between the Operator's IP services 130 and the PCRF 120.
The 3GPP network may be organized using network sharing which is that the radio network is shared. At network sharing, the 3GPP standard provides two reference architectures; GateWay Core Network (GWCN) and Multi-Operator Core Network (MOCN). In GWCN, CN nodes such as an MME or an SGSN are shared between the CN operators in addition to the Radio Access Network (RAN). In MOCN, only the radio access network is shared between the CN operators.
The RAN may support wireless device mobility in connected mode by using a handover procedure. The connected mode is one of two operational modes of the wireless device. The other mode is idle mode. In idle mode, after the wireless device has been switched on, it selects a Public Land Mobile Network (PLMN) to connect to. The wireless device searches for a cell of the selected PLMN that can provide available services and camps on the selected cell. In idle mode, the wireless device is identified by parameters such as International Mobile Subscriber Identity (IMSI), Temporary Mobile Subscriber Identity (TMSI) and Packet Temporary Mobile Subscriber Identity (P-TMSI). The RAN does not have any information about idle devices, i.e. information such as location, bearer information etc. The wireless device stays in idle mode until it transmits a request to establish a radio connection. In connected mode, the wireless device transmits and receives data. The wireless device leaves the connected mode and returns to idle mode when a Radio Resource Control (RRC) connection is released or at RRC connection failure. In connected mode, the RAN has information about the connected devices, i.e. information such as location and bearer information etc.
Legacy Mechanisms at Handover—Handover Procedure
At execution of a handover procedure the RAN node that is currently serving the wireless device selects a suitable target cell and signals to the currently serving core node that the wireless device should be moved using a handover procedure. The handover target selected by the RAN node may include a change of 3GPP access.
When current 3GPP radio access is E-UTRAN the evolved Node B (eNodeB) may have access to an information Handover Restriction List. The Handover Restriction List provides the eNodeB with information about allowed and restricted targets and the eNodeB shall use the information if it is provided.
3GPP is currently discussing to allow the MME to perform MME selection in a heterogeneous MME core network by using the same logic as the SGSN does in a MOCN shared network which uses a Common PLMN. The parameter common PLMN is, according to the 3GPP, a PLMN ID indicated in the system broadcast information as defined for conventional networks, which non-supporting wireless devices understand as the serving operator.
In legacy, a Radio Network Controller (RNC) or Base Station Controller (BSC) routes an unknown wireless device to any available SGSN and allows the SGSN to decide if it will accept the request or not. In case of a reject, the SGSN comprises IMSI of the wireless device in the response back to the RNC/BSC. This allows the RAN node to, based on local configuration, select an appropriate SGSN based on the IMSI.
In current discussion at 3GPP SA2 the proposal is to enable the MME to, based on “type of wireless device”, decide if the MME will accept to handle the wireless device or not.
Similar to the existing solution to non-supporting shared network in the GERAN/UMTS accesses, the proposed E-UTRAN function for MME selection is to allow an MME selected by eNodeB to reply with a reject back to eNodeB when the MME by support of configuration or subscription information detects that the wireless device shall be served by a different type of MME.
The reject instructs eNodeB to reattempt the request to a different MME based on some criteria, and the anticipated result is that the new MME accepts the request.
However, when a source network during handover shall select a target core MME when the target network is a heterogeneous network with MMEs of different types, there is no mechanism to support the source core node MME/SGSN to select an MME that is serving the matching type of wireless device.